1. Field of the Invention
The present invention relates to a substrate processing system in the electronics industry. More specifically, the invention relates to a system and method for supporting substrates in a substrate processing system.
2. Background of the Related Art
Substrates on which physical vapor deposition (PVD), chemical vapor deposition (CVD), etching, electroplating, planarization and other processes are performed are used to manufacture integrated circuits (ICs), flat panel displays (FPDs) and other electronic components. Round substrates, typically known as wafers, are used to create a plurality of ICs by cutting the wafers into individual die after deposition and other processing. The typical size for a semiconductor wafer is about 200 mm with a thickness of less than 0.5 mm and a mass of about 60 grams. Typical substrate processing requires planar support of the substrate to ensure uniform deposition across the substrate surface in the processing chamber. The relatively small size and light weight of the wafers require minimal structural support to retain a planar processing position.
Conceptually, FPDs are produced by similar processes as are performed in the fabrication of ICs, such as etching, deposition, and planarization. Generally, multiple metallic interconnects, liquid crystal cells and other devices are formed on a glass substrate to produce the FPD. The various devices are integrated into a system that collectively is used to create, for example, active matrix display screens in which display states are electrically created in individual pixels on the FPD. Overall processing uniformity across the entire surface of the FPD is critical for the FPD to function properly and defects in the FPD as a whole need to approach zero.
A typical glass substrate has increased in size from about 200 mm by 300 mm to about 680 mm by about 880 mm and a mass of about 2 to about 3 kilograms. The size is continuing to increase as the demand for larger screens or displays increases.
FIG. 1 is a schematic cross-sectional view of a processing chamber 2, such as a CVD chamber having a top 4, bottom 6, sidewalls 8, a support plate 18 and a susceptor 22 disposed therein to support an FPD substrate 12. In general, CVD processing is the formation of a non-volatile solid layer on a substrate by the reaction of vapor phase chemicals, termed "reactants", which contain the required constituents to be deposited. The reactants enter a system and are decomposed and/or reacted on a substrate to form a desired layer of material thereon. Reactive gases are flown through a gas inlet 14 into a gas manifold 16 that is mounted near the top of the chamber. An opening 10 is disposed in the sidewall 8 to allow a robot (not shown) to deliver and retrieve the substrate 12 to and from the chamber. A support plate 18 is coupled to a support stem 20 and supports the susceptor 22. The support plate 18 is typically made of a single rectangular plate of ceramic material, such as aluminum oxide, and closely covers the area of the susceptor 22. The susceptor 22 historically has been made of a single rectangular plate of aluminum and is typically heated with a heater (not shown) with energy supplied from a power source 24. A susceptor sized to accommodate the larger substrates, such as a 680 mm by 880 mm substrate, can have a mass of about 130 kg. Even larger substrates may require a larger susceptor with a mass of about 230 kg.
Typical temperatures for CVD processes can reach up to about 430.degree. C. Aluminum begins to exhibit "liquid" type properties at about 660.degree. C. and, thus, at the operating ranges of the CVD processes, the aluminum susceptor 22 can deflect and "droop" without adequate support. The ceramic material of the support plate 18 has been used to support the ductile aluminum susceptor. However, ceramic is a relatively poor thermal conductor and, thus, demonstrates a temperature gradient between a hotter upper surface of the support plate 18 that contacts the heated susceptor and a cooler lower surface of the support plate 18. The thermal gradient can cause the hotter upper surface of the substrate to expand a greater distance than the cooler lower surface, and as a result, the support plate 18 deflects downwardly at its outer perimeter. Furthermore, as the support plate 18 deflects, the ductile aluminum susceptor deflects in conformance with the deflected support plate. A substrate supported by the susceptor is prone to conform to the susceptor and, thus, also deflects. As a result, the vertical spacing between the gas manifold 16 and the substrate 12 varies between a central section of the substrate having a distance 34 from the manifold and a peripheral region having a greater distance 36. The difference in spacing decreases deposition and other processing uniformity.
Therefore, there remains a need for a system having a support with reduced deflection for substrates, particularly larger substrates.